The present invention relates to a message path mechanism in a coupled system environment having central processing complexes (CPCs) and a coupling facility, and more particularly relates to a message path mechanism wherein, when the coupling facility receives a command from one CPC in the network, the coupling facility verifies that commands other than pathing commands, are received over an active path. The received command may require commands to be addressed to another CPC, the coupling facility locates a proper message path to send the resulting command to the other CPC.
A channel-to-channel adapter (CTC) is described in SA22-7203-0, ESA/390 ESCON Channel-to-Channel Adapter, available from IBM Corp. of Armonk, N.Y. A command received by the CTC control unit is forwarded to the system that previously requested reception by issuing a prepare command. The prepare command must be reissued after each command reception. In the present invention, signal delivery in the activation of a message path is sufficient preparation for receiving a command. Commands can continue to be received so long as the message path remains active. The CTC raises an I/O interrupt. In the present invention, delivery of a command does not cause program interruption.
The partitioning of ports of the Escon director is described in GA23-0354-0, ESCON Director User's Guide, available from IBM Corp. Command information received on a port can only be routed to one of the ports defined in the same partition. Commands are sent in command frames wherein additional routing information is also provided in a header attached to each command frame. The routing is limited to a single destination port. In the present invention, signal delivery maintains complete routing information in a message path table, and one of several paths may be selected to send the command.
Routing tables are defined in GC30-3073-2, Systems Network Architecture Technical Overview, available form IBM Corp., to guide the delivery of information in a network. The routing tables are generated at each node in the network by a network operator and must be manually maintained. In the present invention, a message-path status table is dynamically maintained by the program and the coupling facility as configuration changes occur.